Digit readout device



April 28, 1970 R. Duv Bols, 4JR, ETAL 3,509,402

DIGIT READOUT DEVICE Filed July 5, `1968 ATTORNEYS United States Patent O U.S. Cl. S13- 109.5 10 Claims ABSTRACT F THE DISCLOSURE This invention relates to a vacuum fluorescent readout device which has a perforate anode, the anode having portions of its area covered with a fluorescent material. A mask is provided adjacent the anode which limits activ-ation of the fluorescent material, by electrons emitted from a cathode and controlled by control grids, to selected areas of the anode which form predetermined designs on the surface of the anode. An additional electrode is mounted between the cathode and control grids to create a uniform distribution of electrons, increase the light output from the fluorescent areas, and increase the sharpness and clarity 0f the predetermined designs appearing on the anode.

Prior readout devices include mechanical structures which are slow in operation, and gaseous discharge devices which show indicia in a viewing plane other than at the end of the tube. The -gaseous discharge devices also have the .disadvantage of having fuzzy indicia outlines which often make the indicia hard to read, along with the further disadvantages of requiring an appreciable amount of time for their actuation, The gas-filled readout devices also require the making and breaking of considerable current when transferring from one character to another.

Application Ser. No. 479,425, now issued as Patent No. 3,406,288 and assigned to the same assignee as the present invention, discloses a readout device having a plurality of cathodes, a plurality of control grids and an insulative mask having apertures therein adjacent a screen anode having fluorescent material deposited therein. The cathode, control grids, anode and mask are mounted within an evacuated glass enclosure. It was found that in order to obtain satisfactory operation of this readout device, it was necessary to provide a plurality of cathodes, one for each of the apertures used to form the indicia on the anode. The best results were 0btained with these cathodes mounted adjacent each aperture along the line of sight comprising the anode screen and control grid, and as a res-ult the red glow of the hot cathode could be seen through the anode screen. This red glow is especially evident through those apertures not being used to form part of the indicia being viewed at any one time. Additionally, the illumination present on the iiuorescent surface of the anode was not uniform in brightness over the whole indicia, the intensity of illumination noticeably diminishing toward the ends of each aperture of the indicia.

A further problem was caused by the fact that the cathodes had to be mounted in close proximity to the control grids for best results, and the device consequently was sensitive to jolts, impacts or other physical shock which tended to displace the cathode into short-circuiting contact with the adjacent control grid.

It has now been discovered that the above-described disadvantages are overcome if an additional electrode is positioned between the control grids and the cathode. It has been found that by the use of such an electrode mounted between the cathode and the control grids, the necessity of providing a separate cathode for each aper- 3,509,402 Patented Apr. 28, 1970 ture in the mask can be eliminated. Surprisingly and unexpectedly, it has been found that the fluorescent intensity of the anode increases and becomes uniform over the entire indicia being displayed on the anode even though the number of cathodes are significantly reduced. Also, the oultine and sharpness of the indicia are not fuzzy and are considerably improved over that previously obtained. Furthermore, it has been noted that by the use of this additional electrode, it is possible to use one and preferably two cathodes mounted in misalignment with the apertures of the mask and out of the line of sight of an observer and still achieve very bright and uniform illumination of the anode surface with substantially no fuzziness. By mounting the cathode out of the line of sight of an observer, the red glow emanating from the hot cathode will not be seen by the observer, thereby eliminating this particular problem. It has' also been found that by using the additional electrode, it is possible to provide additional apertures in the mask for forming such aded indicia as a decimal point and an apostrophe which show up with a clarity and brilliance equal to any part of the indicia itself. This was not possi-ble with the prior device of this sort without providing an additional cathode for each additional indicia. Finally, it has been found that use of the additional electrode allows the cathode to be spaced more distantly from the control grids to avoid the sensitivity to shock and short-circuiting described above.

The mechanisms by which these advantages are gotten are not completely understood at this time. However, it will be seen from the foregoing that many important advantages flow from the use of an additional electrode mounted between the cathode and control grids of a vacuum readout device of the type described.

For a better understanding of the present invention, reference is made to the following drawings which illustrate a preferred embodiment of the invention and in which like numerals refer to like parts.

FIG. 1 is a cross-sectional view of the readout device taken along an axial plane and showing the components.

FIG. 2 is a cross-sectional View of the readout device of FIG. l taken along line 2-2 of that figure.

FIG. 3 is a plan view of a portion of the anode to an enlarged scale.

FIG. 4 is a cross-sectional view of the electrodes of the device showing the mask and the general path taken by the electrons.

FIG. 5 is a schematic diagram showing how the components are connected. Only one of eight control grids are shown in this figure.

FIG. 6 is a series of views showing one set of indicia which can be produced by seven segments of mask apertures and seven corresponding control grids.

Referring now to FIGS. l, 2, 3 and 4, a glass envelope 10 is shown enclosing a cathode 11 shown in two parts in FIG. 1, a screen anode 12 which may comprise woven nickel wire, an apertured mask 13, a plurality of control grids 14 and an additional electrode 15. The cathode 11, screen anode 12, control grids 14 and additional electrode 15 are connected to lead-in conductors 19 sealed into the wall of envelope 10 for connection to an external circuit. The electrode 15 is mounted between the cathode 11 and the plane of the control grids 14, and for reasons not completely understood, causes the electrons emanating from the cathode to pass in substantially equal quantities through each aperture which is open to electron flow at a given instant.

In the preferred construction, the anode 12 is made of a screen material having fluorescent material 16 deposited on the wire portions of the screen, thereby leaving openings within the anode through which electrons emanating from the cathode 11 may pass. The uorescent material is preferably deposited in discrete amounts substantially corresponding to the size of each aperture 20 in the mask 13. Electrons passing through the anode screen material are repulsed by an electrical eld applied to a tin oxide coating 17 deposited on the inside of the glass shield 18 to strike the upper fluorescent surface of anode 12 and energize the fluorescent particles 16 thereon. The coating 17 is transparent and allows the user to see the fluorescent surfaces below it.

The mask 13 is made of an insulating material and is formed with apertures which correspond in number and size to the fluorescent areas on the anode 12. One arrangement is shown in FIG. 2 where seven elongated apertures 20 are used to form digits from 0l to 9 as indicated in FIG. 6. In addition, a decimal point aperture 21 and an apostrophe aperture 22 are provided. FIG. 2 shows, in dotted lines, the position of the two cathode filaments 11. In contrast to prior readout devices, only two cathode filaments 11 are used in the preferred embodiment to energize the anode 12 through each of the apertures 20' in the mask 13.

The operation of the readout device will be understood from FIGS. 4 and 5. With applied voltages as indicated in IFIG. and switch 23 in the full line position, a dark tube is maintained by applying volts to all nine of the control grids 14. To show a digit, the control grids adjacent to the desired apertures are switched to connect them to ground (dotted line position of switch 23) and the bombardment of the electrons moving through the apertures 20 are repulsed by oxide layer 17 to cause the fluorescent material 16 on the anode 12 to iluoresce. As previously noted, the additional electrode 1S causes electrons emitted from the misaligned cathodes 11 to pass uniformly through the apertures 20 to produce substantially equal fluorescent intensity of the fluorescent material 16 on the anode 12, regardless of the number of apertures which are forming the indicia at any one time.

In FIG. 5, a single switch 23 is shown as the means for showing a lighted area. To display any one of the ten digits shown in FIG. 6, at least seven switches are required. The readout device is intended for use with com puters and other similar electronic circuits where mechanical switches are generally not used. The grids may be activated by thyratrons, silicon controlled rectiers, or other pulse forming circuits.

While the preferred embodiment includes an anode of woven wire construction, a perforate metal sheet may be used, having equally spaced perforations produced by etching or punching.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

What is claimed is:

1. A readout device comprising: a sealed evacuated envelope; at least one cathode, an anode and a plurality of control electrodes; an insulator positioned between the cathode and the anode and formed with a plurality of apertures to allow passage of electrons from said cathode to said anode; a fluorescent material deposited on the anode for the generation of a light pattern when said iluorescent material is bombarded with electrons, said control electrodes respectively positioned adjacent said apertures for selectively controlling the passage of electrons through said apertures, and an additional electrode positioned between said cathode and said control electrodes to assure substantially equal uorescent intensity of said fluorescent material on said anode.

2. A readout device as in claim 1 wherein two cathodes are used, said two cathodes being positioned under said insulator out of the line of sight between said apertures and said anode.

3. A readout device as in claim 1 wherein said apertures are arranged in a preselected pattern for the formation of indicia which includes a decimal point and an apostrophe.

4. A readout device as in claim 1 wherein said additional electrode is at a potential greater than that of said cathode but less than that of said control electrodes during control of electron passage by said control electrodes.

5. A readout device as claimed in claim 1 wherein said anode is made of metal and is formed with a plurality of spaced apertures, said lluorescent material deposited on said anode.

6. A readout device as claimed in claim 1 wherein a transparent plate is positioned within the envelope in spaced relation to the anode and wherein a transparent y insulator.

9. A readout device as claimed in claim 1 wherein the anode, the cathode, the additional electrode and all the control electrodes are connected to lead-in conductors sealed into the envelope wall for connection to an external circuit.

10. A readout device as claimed in claim 1 wherein the anode is made of woven nickel wire.

References Cited UNITED STATES PATENTS 3,406,288 10/ 1968 Du Bois et al S13-109.5

JAMES W. LAWRENCE Primary Examiner D. OREILLY, Assistant Examiner U.S. Cl. X.R. 250-217 

